The present invention relates to a golf ball. More particularly, it relates to a golf ball having soft and good shot feel, high rebound characteristics and excellent abrasion resistance when hit by an iron club.
Recently, ionomer resin has been widely used for cover material of golf balls. Particularly, it has been almost used for a base resin of the cover of solid golf balls, such as two-piece golf ball and three-piece golf ball. This is because the ionomer resin is superior in durability, cut resistance, rebound characteristics, etc. and it is easily processed.
However, since the ionomer resin has high hardness and rigidity, the resulting golf ball is poor in shot feel and controllability in comparison with balata (transpolyisoprene)-covered thread wound golf ball. In order to improve shot feel and controllability of the ionomer-covered golf balls, it is attempted to soften the ionomer resin by various means.
For example, Japanese Patent Kokai Publications Nos. 308577/1989, 314463/1992, 3931/1993, 327793/1994, 249/1998 and the like propose that the ionomer resin having high rigidity is mixed with ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with sodium ion, zinc ion or magnesium ion to soften it in order to improve the shot feel and controllability.
However, when the mixture of the soft ionomer resin is used, the hardness of the cover is low, and the flexural modulus of the cover is low. Thereby the rebound characteristics and flight distance of the resulting golf ball. In addition, since the cover is soft, the spin amount is high, which improves the controllability when hit by an iron club. However, since the contact area of a face surface of the golf club with golf ball is large, it is problem that the surface of the golf ball easily suffers an abrasion.
In order to solve the problem, it has been proposed to select the combination of neutralizing metal ions of the ionomer resins in the mixture of the hard ionomer resin and soft ionomer resin (for example, Japanese Patent No. 2897697, Japanese Patent Kokai Publications No. 248/1998 and the like).
In Japanese Patent No. 2897697, a golf ball, which a blend of ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with zinc ion or sodium ion and ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with magnesium ion is used as a cover material, is described. In Japanese Patent Kokai Publications No. 248/1998, a golf ball, which a blend of ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with magnesium ion and ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with magnesium ion is used as a cover material, is described. In the golf balls described in the both patent documents, the technical effects of improving the abrasion resistance and rebound characteristics, while maintaining good shot feel and controllability, by using the blend of the hard ionomer resin and the soft ionomer resin for the cover material, is obtained.
However, a golf ball, which is sufficient to improve the abrasion resistance and rebound characteristics, has been not obtained by the method of using the blend of the hard ionomer resin and the soft ionomer resin. It has been required to provide the golf ball, which the abrasion resistance and rebound characteristics are improved still more, while maintaining good shot feel and controllability.
A main object of the present invention is to provide a golf ball having soft and good shot feel, high rebound characteristics, and excellent abrasion resistance when hit by an iron club.
According to the present invention, the object described above has been accomplished, in a golf ball comprising a core and at least one layer of cover covering the core, by employing the outmost layer of the cover which is formed from three specified ionomer resins obtained by neutralizing with specified metal ions, and adjusting a Shore D hardness of the outmost layer of the cover to a specified range, thereby providing a golf ball having soft and good shot feel, high rebound characteristics, and excellent abrasion resistance when hit by an iron club.
The present invention provides a golf ball comprising a core and at least one layer of cover covering the core, wherein the outmost layer of the cover is formed from a base resin mainly containing the mixture of
(i) ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with magnesium ion,
(ii) ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with sodium ion, and
(iii) ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with zinc ion, and
the outmost layer of the cover has a Shore D hardness of 45 to 60.
In order to practice the present invention suitably, it is preferable that the ionomer resin (i) have a flexural modulus of 10 to 100 MPa, the ionomer resins (ii) and (iii) have a flexural modulus of 200 to 500 MPa and a Shore D hardness of 55 to 70, and a weight ratio [(ii)/(iii)] of the ionomer resin (ii) to the ionomer resin (iii) be within the range of 30/70 to 80/20.
The present inventors studied the type of ionomer resin used for a cover material of golf ball and the type of neutralizing metal ion of the ionomer resin in order to improve the abrasion resistance and rebound characteristics of the golf ball, which is the object of the present invention. As a result, they found that the golf ball using the ionomer resin obtained by neutralizing with sodium ion, magnesium ion or zinc ion in order is superior in rebound characteristics (sodium ion greater than magnesium ion greater than zinc ion), and the golf ball using the ionomer resin obtained by neutralizing with magnesium ion or zinc ion has good abrasion resistance, but the golf ball using the ionomer resin obtained by neutralizing with sodium ion has poor abrasion resistance, in addition to the selection of a combination of ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with metal ion and ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with metal ion.
Therefore, for example, in Japanese Patent No. 2897697 described above, from the performance of the golf ball using the ionomer resin obtained by neutralizing with magnesium ion, the rebound characteristics are degraded by blending the ionomer resin obtained by neutralizing with zinc ion, and the abrasion resistance is degraded by blending the ionomer resin obtained by neutralizing with sodium ion. In Japanese Patent Kokai Publications No. 248/1998 described above, the resulting golf ball has good abrasion resistance, but sufficient rebound characteristics are not obtained, because of blending two ionomer resins obtained by neutralizing with magnesium ion.
On the other hand, the mixture of
(i) ethylene-(meth)acrylic acid-acrylic ester terpolymer ionomer resin obtained by neutralizing with magnesium ion,
(ii) ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with sodium ion, and
(iii) ethylene-(meth)acrylic acid copolymer ionomer resin obtained by neutralizing with zinc ion is used for the cover material of the present invention. In the present invention, from the performance of the golf ball using the ionomer resin obtained by neutralizing with magnesium ion (i), insufficiency in the abrasion resistance and rebound characteristics is covered by blending the ionomer resins obtained by neutralizing with sodium ion (ii) and zinc ion (iii), and it is possible to improve only the rebound characteristics, while maintaining excellent abrasion resistance, by adjusting a weight ratio [(ii)/(iii)] of the both ionomer resins to a specified range.